<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">

<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<meta name="description" content=" HTML页面">
<title>第5课 用css来控制</title>
<style>
div {
	/* width: 300px; */
	height: 300px;
	background: blue;
}

/* 先在body中写出div的id，再在这里用#井号引用  */
#main {
	background: green;
}

#footer {
	background: gray;
}
</style>
</head>

<body>
	<!-- id是唯一的 -->
	<div id="header"></div>
	<div id="main"></div>
	<div id="footer"></div>
</body>


</html>